At present, voice communication using a network such as the Internet has been actively conducted by the use of a VoIP technology.
In communication over a network such as the Internet, in which the communication quality is not assured, a packet loss that a packet is lost during transmission frequently causes a phenomenon (voice loss) that a part of voice data, which is supposed to be received in a time series under normal circumstances, is lost. When a voice loss occurs, if the voice data is decoded as it is, voice is frequently interrupted to degrade the voice quality. A technology disclosed in non-patent document 1 to be described below has been already known as a method for compensating this degradation.
In this method, the occurrence of a voice loss is monitored for each voice frame (packet) which is a decoding processing unit, and every time the voice loss occurs, compensation processing is performed. In this compensation processing, voice data after decoding a series of encoded voice data is stored in an internal memory or the like, and when a voice loss occurs, a fundamental period near a position where the voice loss occurs is obtained on the basis of voice data read from the internal memory. Then, the voice data is extracted from the internal memory to perform interpolation in regard to a frame in which voice data needs to be interpolated (compensated) because of the voice loss, so that the starting phase of the frame matches the ending phase of an immediately preceding frame to be able to secure continuity in a waveform period (fundamental period).
Meanwhile, technologies described in non-patent documents 2 and 3 to be described below are known as a method of voice communication over a network.
In the technology described in the non-patent document 2, voice data is transmitted in a single band, but the technology described in the non-patent document 3 relates to a band division method (SB-ADPCM) in which voice data of a wider band (for example, a band of 8 kHz) than usual is divided into two bands and is transmitted so as to realize voice communication of high quality.
Non-patent document 1: ITU-T Recommendation G. 711 Appendix I
Non-patent document 2: ITU-T Recommendation G. 711
Non-patent document 3: ITU-T Recommendation G. 722